Have you told Kobo about your friend's with the origninal Kobo as compared to you? This is helpful info to the company means that there is something in the model that is causing trouble in the button so they can go out looking for the problem if they know there is a high probablity that they will find something wrong.

We are a two whit Kobo, one black Kobo family and have, so far,not had a problem. I do wonder if there was a bad batch, and your store happened to get them. Fortunately, manufacturer's defects are covered for a year. It's hard to believe that the Kobo reader is still quite a bit shy of a year old.